Abstract
Sleep-related masticatory muscle activity has been reported to occur in association with physiological changes of sleep process (e.g., arousal) in humans. This study aimed to assess masticatory muscle activities during wakefulness and sleep in the guinea pig. Animals were prepared for chronic experiments to monitor electroencephalogram, electro-occulogram and electromyograms from dorsal neck, bilateral masseter and digastric muscles in freely moving states. After the animals recovered from surgery, these signals were recorded for 6 to 8 hours during light-phase. Sleep stages were scored for every 10-second epoch. Muscle activities were integrated for each epoch and compared between ingestion and three quiet states (quiet wakefulness, non-REM and REM sleep). All muscles showed the highest activity during ingestion. Neck muscle activity decreased clearly from quiet wakefulness to non-REM sleep and further to REM sleep. Masticatory muscle activity was 5 to 8 times lower in quiet states than during ingestion. However, the difference between the quiet states was less evident in the masticatory muscles. These results suggest that, when epoch-based analysis was done, masticatory muscle activity in the quiet states is usually very low and the state-dependent muscle activity may be different between masticatory and neck muscles. [J Physiol Sci. 2006;56 Suppl:S208]
